Devices for switching electric current are conventionally of a mechanical nature and as such embody a number of disadvantages, for example the generation of significant transients such as sparks on actuation of the switch.
It has been proposed to provide polymer compositions capable of providing a variable electrical conductivity effect.
DE 195 10 100 A1 discloses elastically moldable resistors which are either non-conductive in the quiescent state, becoming conductive on the application of pressure, or are conductive in the quiescent state, becoming less conductive under tension. Significantly high pressures of the order of 100 Kgf/cm.sup.2 are required to decrease the resistance to 2-3 ohm/cm, such pressures being two orders of magnitude above human `touch` pressure which is typically in the range of 300 to 600 gf/cm.sup.2. Thus such devices are unsuitable for electrical switches relying on finger contact to change electrical resistance from open circuit to low resistance values.
DE 27 16 742 discloses pressure sensitive elastomer compositions that change electrical resistance from a semi-conducting state of typical resistivity 10.sup.3 ohms/cm to a low resistance state of typical resistivity 10 ohms/cm by the application of high pressures, typically 5-15 Kgf/cm.sup.2. Again such materials are unsuitable for practical finger switching devices.